Biology is the natural science that involves the study
of life and living organisms, including their physical
structure, chemical composition, function, development and evolution.
Modern biology is a vast field, composed of many branches. Despite the
broad scope and the complexity of the science, there are certain unifying
concepts that consolidate it into a single, coherent field. Biology recognizes
the cell as the basic unit of life, genes as the basic unit
of heredity, and evolution as the engine that propels the
creation of new species. Living organisms are open systems that
survive by transforming energy and decreasing their local entropy to maintain a stable and
vital condition defined as homeostasis. See glossary of biology.
Sub-disciplines
of biology are defined by the scale at which life is studied, the kinds of
organisms studied, and the methods used to study them: biochemistry examines
the rudimentary chemistry of life; molecular biology studies the
complex interactions among biological molecules; cellular biology examines
the basic building-block of all life, the cell; physiology examines
the physical and chemical functions of tissues, organs, and organ
systems; ecology examines how organisms interact in their environment;
and evolutionary biology examines the processes that produced the
diversity of life
Biology in essence is the story of life on earth. While individual organisms die without fail, species continue to live through millions of years unless threatened by natural or anthropogenic extinction. Reproduction becomes a vital process without which species cannot survive for long. Each individual leaves its progeny by asexual or sexual means. Sexual mode of reproduction enables creation of new variants, so that survival advantage is enhanced. This unit examines the general principles underlying reproductive processes in living organisms and then explains the details of this process in flowering plants and humans as easy to relate representative examples. A related perspective on human reproductive health and how reproductive ill health can be avoided is also presented to
complete our understanding of biology of reproduction.
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